1. Field of the Invention
The present invention relates to a process for the production of a casing with protective bellows for a transmission device, such as a transmission joint, comprising at least two shafts movable axially and/or angularly relative to each other, this casing with bellows, for which at least one portion of the bellows is radial, having at each open end a securement section to the transmission device, as well as a casing with protective bellows obtained particularly by the practice of this process.
2. Description of the Related Art
Different systems for the transmission of movement of a drive shaft to a driven shaft are at present used, preferably with a cardan joint, in particular in the automotive industry in which more and more uses had, for the drive of the wheels from the motor, to devices with homokinetic joints. In such joint devices, a mechanical assembly is lubricated permanently by a mass of grease which is enclosed in a protective bellows. The latter must be able on the one hand to deform elastically in several directions and on the other hand to keep its properties despite multiple causes for damage which can arise in the course of the life of the vehicle. Thus, it has been known for a long time that damage to the bellows is due in particular to the shocks arising from projections of road paving particles which give rise to fissures in the elastomeric material used, or to friction of the elements of the bellows against each other.
There exists in the prior art two types of casings with bellows, namely, on the one hand, casings with protective bellows whose bellows are so-called axial, as shown in FIG. 2, so as to permit essentially a small axial deformation of said bellows, on the other hand casings with radial bellows (FIG. 1) permitting radial, axial or angular displacements of the transmission device. In the case of axial bellows, the wall of the envelope is formed by undulations or holes whose flanks extend substantially parallel to the longitudinal axis of said casing (see FIG. 2). This type of casing has the advantage of being easy to produce because of the absence of counter-clearances. Thus, for this type of casings with bellows, numerous production techniques can be used. However, casings with bellows most often used nowadays are shown in FIG. 1 because of their possibilities for deformation. In this case, at least a portion of the bellows of said casing are radial. In the second family of casings with bellows, the body of the casing, constituted by a tubular body disposed about an axis longitudinal of said casing, is delimited by an undulant wall whose flanks of the folds extend substantially in an essentially radial direction relative to the longitudinal axis of said wall. This arrangement of folds of the bellows permits both an axial and an angular deformation of the bellows, rendering such casings with bellows applicable to a large number of transmission mechanisms.
To permit optimum deformation of such a casing with bellows, these casings have for a long time been produced by molding or injection of vulcanized rubber. However, because of the low mechanical resistance of rubber, the producers have sought to replace rubber with materials of greater rigidity characteristics. As a result, the usual technique applicable to rubber had been replaced by injection/blowing techniques such as described in French patent 2.610.566. In addition to the blow injection technique described in French patent 2.610.566, other blowing techniques have been developed. Thus, generally and as shown in French patent 2.606.849, during production, the molding material, constituted by a thermoplastic elastomeric tube in a pasty condition, is blown. The thermoplastic elastomer presses itself against the cold walls of the mold which represent the external surface of the bellows. Upon opening, the two parts of the mold release the obtained bellows. This blowing process represents a complicated and costly mode of production which is not yet perfected from a point of view of quality. Thus, the correct distribution of thickness of material along the bellows is difficult to obtain because it depends on a number of factors. As a result, there is required on the one hand the use of an excess of material so as to guarantee minimum thickness, on the other hand to provide unitary monitoring of the pieces.
There are thus sought nowadays processes permitting the production of casings with bellows having radial bellows with substantial counter-clearances and made of a relatively rigid material, in particular to resist high temperatures and to increase the mechanical resistance of said casing.